This is a pretty cool idea. Very easy project for an archaeology aficionado. I think I might give it a try once I get my free time back and I have the luxury of goofing off.
They're just using floor slate, the same you could buy at any home improvement store for $2 a square foot.
I'm guessing these are students of archaeologist Jonathan Thomas.
(Clearly some students are better than others!!)
And then the finishing touches.